1. Field of the Invention
South African No. 72-3212, an application for letters patent filed May 10, 1972 by The Procter & Gamble Company which was laid open for public inspection on Feb. 23, 1973 and sealed on June 4, 1973, which is herein incorporated by reference, disclosed a photoactivated bleaching process whereby stains are removed from textiles through the use of detergent solutions containing sulfonated zinc phthalocyanine. These solutions are irradiated with visible light and exposed to oxygen during the washing and bleaching process. A preferred photoactivator was said to be sulfonated zinc phthalocyanine which was free from unsulfonated zinc phthalocyanine. Variation in the degree of sulfonation of zinc phthalocyanine was said not to affect the efficacy of the material as a photoactivator.
The instant invention recognizes the fact that sulfonated zinc phthalocyanine is not a single entity but may be any of four species: mono-, di-, tri-, and tetra-sulfonated zinc phthalocyanine. The characteristics of each species have been determined, and particular mixtures have been found to have unexpectedly beneficial results in the aforesaid photoactivated bleaching process.
2. Prior Art
Zinc phthalocyanine was first prepared by Sir Reginald Linstead and co-workers at the Imperial College of Science and Technology of London in the 1930's, as reported in Barrett, Dent, and Linstead, "Journal of the Chemical Society," (1936) at page 1719. Then, as now, the zinc compound has tended to live in the shadow of its copper analog which is now produced in quantities of millions of pounds per year for use as pigments and dyes. The chemistry of the zinc compound is similar to that of the copper compound in that each can be made by similar processes; each occurs in three crystalline phase structures; and each undergoes similar chemical reactions such as chlorination and sulfonation. However the properties of the analogs are sufficiently distinct that it is mainly the copper compounds that have found commercial utilization.
Unsubstituted metal phthalocyanines are soluble in water to an unusually low degree and are used as pigments. Water solubility can be achieved to a progressively greater degree by introduction of hydrophilic groups such as sulfo, carboxy, or chloromethyl groups into the phthalocyanine molecule. This is most conveniently done by sulfonation, and up to four sulfo groups can be introduced by the use of hot oleum. Sulfonated phthalocyanines are useful as direct dyes because they have an affinity for cellulose in the form of either cotton or paper pulp. Copper is the only metal used commercially in this way, and produces dyes that are blue to yellow-green in color depending on the other substituents in the molecule. A good reference work on phthalocyanine pigments and dyes is "The Chemistry of Synthetic Dyes and Pigments," edited by H. A. Lubs, Reinhold, N.Y. (1955).